expr command help

Shell Programming and Scripting
1

I'm trying to check if a variable'd string is only one character and use that in an if statement the only way I could find is:
$expr "${var}" : . # expr STRING : regrep
where the "." is the grep wildcard for any single character.

Whats wrong with my code here and is there a better way to check if the input is 1 character?

also if i want to pass a variable into a arguement of another function like expr but the content of the variable might cause a syntax error if treat as other then a string, how do i escape ("\") the contents of the variable and not the variable call itself.

2

Hi.

You could say:

if [ "${#var}" -eq 1 ]; then
  echo only one character long
else
  ...
fi

I've never found any cause to use "expr". Any modern shell has better ways of handling whatever it was good for.

3

Thank you.

---------- Post updated at 06:32 PM ---------- Previous update was at 06:21 PM ----------

also if i want to pass a variable into a arguement of another function like expr but the content of the variable might cause a syntax error if treat as other then a string, how do i escape ("\") the contents of the variable and not the variable call itself.

4

There's usually no compelling reason to use expr at all.

The man page says:

I guess that part is left up to the imagination.

If that means using shell, eval, or sed, or whatever, then, whichever way you like.

$ X="\"3\""
$ echo $X
"3"

$ expr $X + 1
expr: non-numeric argument

$ eval expr $X + 1
4

$ Y=${X//\"}
$ echo $Y
3

$ expr $Y + 1
4

$ expr ${X//\"} + 1
4

etc.